Advertising Unreachable Links in OSPF
draft-ietf-lsr-ospf-ls-link-infinity-11
| Document | Type | Active Internet-Draft (lsr WG) | |
|---|---|---|---|
| Authors | Liyan Gong , Weiqiang Cheng , Changwang Lin , Acee Lindem , Ran Chen | ||
| Last updated | 2025-09-28 | ||
| Replaces | draft-gong-lsr-ospf-unreachable-link | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Yang Validation | 0 errors, 0 warnings | ||
| Reviews |
RTGDIR Early review
(of
-07)
by Cheng Li
Has issues
YANGDOCTORS Early review
(of
-07)
by Ladislav Lhotka
Ready w/issues
OPSDIR Early review
(of
-07)
by Dhruv Dhody
Has issues
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | Yingzhen Qu | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | yingzhen.ietf@gmail.com |
draft-ietf-lsr-ospf-ls-link-infinity-11
LSR Working Group L. Gong
Internet-Draft W. Cheng
Updates: 6987, 8770 (if approved) China Mobile
Intended status: Standards Track C. Lin
Expires: 1 April 2026 New H3C Technologies
A. Lindem
Arrcus, Inc.
R. Chen
ZTE Corporation
28 September 2025
Advertising Unreachable Links in OSPF
draft-ietf-lsr-ospf-ls-link-infinity-11
Abstract
In certain scenarios, it is necessary to advertise OSPF links that
are not applicable to the default SPF (Shortest Path First)
calculation for other purposes. In order to advertise these links
and not use them in the base SPF calculation, the metric
LSLinkInfinity (0xffff) is used to specify that the link is
unreachable.
Stub Router Advertisement (RFC 6987) defines MaxLinkMetric (0xffff)
to indicate a router-LSA link should not be used for transit traffic.
When an OSPFv2 router supports the Unreachable Link support
capability defined in this document, OSPFv2 Stub Router links are
advertised as MaxReachableLinkMetric (0xfffe) rather than
MaxLinkMetric (0xffff). This document updates RFC 6987 and RFC 8770
with respect to the advertisement of MaxReachableLinkMetric rather
than MaxLinkMetric.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on 1 April 2026.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Case 1: Traffic Engineering . . . . . . . . . . . . . . . 3
2.2. Case 2: Flexible Algorithm . . . . . . . . . . . . . . . 4
3. LSLinkInfinity-Based Solution . . . . . . . . . . . . . . . . 5
3.1. Unreachable Link Advertisement . . . . . . . . . . . . . 5
3.2. Unreachable Link Backward Compatibility . . . . . . . . . 5
3.3. Stub Router Advertisement Backward Compatibility . . . . 6
4. Operational Considerations . . . . . . . . . . . . . . . . . 7
4.1. Configuration Parameters . . . . . . . . . . . . . . . . 7
4.2. YANG Data Model . . . . . . . . . . . . . . . . . . . . . 7
4.2.1. Tree for OSPF Functional Capability . . . . . . . . . 8
4.2.2. Tree for OSPF Advertising Unreachable Links . . . . . 8
4.2.3. IANA Module for OSPF Functional Capability Bits . . . 9
4.2.4. YANG Module for OSPF Functional Capability . . . . . 11
4.2.5. YANG Module for OSPF Advertising Unreachable Links . 14
5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
6.1. Registering OSPF Router Functional Capability Bits . . . 17
6.2. Registering YANG Modules . . . . . . . . . . . . . . . . 18
6.3. IANA Module for OSPF Functional Capability Bits . . . . . 19
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 20
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1. Normative References . . . . . . . . . . . . . . . . . . 20
9.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
In certain scenarios, it is necessary to advertise OSPF links that
are not applicable to the default SPF calculation for other purposes.
For example, a link may be available for Traffic Engineering (TE)
purposes but not suitable for hop-by-hop routing. Another example is
an OSPF link used exclusively by a Flexible Algorithm [RFC9350] but
excluded from the default algorithm.
In order to advertise these links as unreachable, the metric
LSLinkInfinity (0xffff) is used to specify that the link is
unreachable and OSPF routers supporting this specification will
exclude the link from SPF calculations (subject to backward-
compatibility constraints, refer to Section 3.2).
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Use Cases
2.1. Case 1: Traffic Engineering
A network topology is shown in Figure 1. The OSPF link between Node
A and E is only to be used for traffic engineering. Since the OSPF
link is advertised by default, it will be included in the base SPF
calculation for the default topology and may be used for hop-by-hop
routing in the default topology.
TE Link
---------
/ \
/ \
A------C------E
| | |
| | |
| | |
B------D------F
Figure 1: Network Topology
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2.2. Case 2: Flexible Algorithm
A network topology is shown in Figure 2. The links between nodes A
and B and between C and D are to be used exclusively for a flex-
algorithm [RFC9350] devoted to specific traffic. These links have an
Extended Administrative Group (EAG) [RFC7308] attribute specifying
the "Red" color.
******
A------C------E
|* |* |
|* |* | ******: "Red" link
|* |* |
B------D------F
******
Figure 2: Network Topology
Flex-Algorithm 128 is enabled on Nodes A, B, C, and D, with an EAG
rule including "Red" and the Metric-Type is designated to be a type
other than the IGP metric. OSPF will compute routes for Flex-
Algorithm 128 using these links. The topology associated with Flex-
Algorithm 128 is shown in Figure 3.
A******C
* *
* *
* *
B******D
Figure 3: Topology of Flex-Algorithm 128
The "Red" links that are used by Flex-Algorithm 128 calculation.
However, these "Red" links are also included in the default algorithm
calculation [RFC9350] since they are reachable. Note that links used
by the default algorithm are omitted from Figure 3 for clarity.
If the IGP metrics for all the "Red" links are advertised as
unreachable, they will be excluded from the default SPF calculation
as shown in Figure 4, This allows the "Red" links from A to B and C
to D to be used exclusively by the Flex-Algorithm 128 calculation.
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A------C------E
| | |
| | |
| | |
B------D------F
Figure 4: Base SPF Topology Excluding Unreachable Links
3. LSLinkInfinity-Based Solution
3.1. Unreachable Link Advertisement
This document specifies that if the IGP metric of a link is
advertised as LSLinkInfinity (0xffff), it MUST NOT be considered
during the associated SPF computation. This applies to both the
Flex-Algorithm SPF and the base SPF as long as LSLinkInfinity is
specified for the IGP metric.
While the interpretation of LSLinkInfinity is only required in the
base topology as other topologies are optional [RFC4915], OSPF
routers supporting this specification MUST consistently interpret
LSLinkInfinity as unreachable during the associated SPF computation.
This applies to both the Flex-Algorithm SPF and the base SPF as long
as LSLinkInfinity is specified for the IGP metric.
An IGP metric with LSLinkInfinity indicating a link is unreachable is
applicable to the following TLVs/LSAs:
* The Router-LSA [RFC2328] [RFC5340]
* The OSPFv2 Extended Link TLV of OSPFv2 Extended Link Opaque LSA
[RFC7684]
* The Router-Link TLV of OSPFv3 E-Router-LSA [RFC8362]
3.2. Unreachable Link Backward Compatibility
Prior to this specification, OSPF treated links advertised as
LSLinkInfinity as reachable [RFC2328]. Hence, partial deployment of
this specification may result in routing loops due to inconsistent
interpretation of LSLinkInfinity. For example, in the network shown
in Figure 5, link D-F is advertised with LSLinkInfinity
(65535/0xffff). Router B supports LSLinkInfinity as unreachable, but
router A doesn't. Router A considers link D-F as reachable, and the
shortest path to F is A->B->D->F. Router B considers link D-F as
unreachable, and the shortest path to F is B->A->C->E->F. As a
result, A forwards the packets to B, but B returns them to A, which
results in a routing loop.
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40000 40000 Traffic: A->F
A------C------E A considers link D-F as reachable
| | A's shortest path: A->B->D->F
5| |5 B considers link D-F as unreachable
| | B's shortest path: B->A->C->E->F
B------D------F
5 65535
Figure 5: Inconsistent LSLinkInfinity Interpretation Causing Loops
To provide backward compatibility, this document defines that routers
supporting LSLinkInfinity for unreachable links MUST advertise a
Router Information (RI) LSA with a Router Functional Capabilities TLV
[RFC7770] including the following Router Functional Capability Bit:
+=====+==========================+
| Bit | Capabilities |
+=====+==========================+
| TBA | Unreachable Link support |
+-----+--------------------------+
Table 1
OSPF Routers MUST NOT treat links with an advertised metric of
LSLinkInfinity as unreachable unless all routers in the OSPF area
have advertised this capability. If all OSPF Routers in the area
have advertised this capability, then links with an advertised metric
of LSLinkInfinity MUST be treated as unreachable. Upon detection of
a change in the number of routers in the area not supporting the
Unreachable Link support capability changes to 0 or from 0 to greater
than 0, all OSPF routers in the area MUST recalculate their routes.
3.3. Stub Router Advertisement Backward Compatibility
Stub Router Advertisement [RFC6987] defines MaxLinkMetric (0xffff) to
indicate a router-LSA link should not be used for transit traffic.
When an OSPFv2 router supports the Unreachable Link support
capability defined in this document, the OSPFv2 stub router
MaxLinkMetric (0xffff) MUST be updated to MaxReachableLinkMetric
(0xfffe). This document updates [RFC6987] and [RFC8770] with respect
to the advertisement of MaxReachableLinkMetric rather than
MaxLinkMetric.
When an OSPFv2 router supports [RFC6987] and the Unreachable Link
support capability defined in this document, it MUST also support
advertisement all its non-stub links with a link cost of
MaxReachableLinkMetric (0xfffe). Since MaxLinkMetric will not be
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used to indicate a link is unreachable unless all OSPFv2 routers in
the area support this specification as specified in Section 3.2, all
routers in the area will also support the usage of
MaxReachableLinkMetric to discourage the usage of stub router links
for transit traffic.
An OSPFv3 router can simply advertise R-bit in its router-LSA options
[RFC5340] to prevent usage stub router links for transit traffic.
Similarly, OSPFv2 routers supporting [RFC8770] can advertise the
H-bit in the router-LSA options.
4. Operational Considerations
4.1. Configuration Parameters
Support of the Unreachable Link support capability SHOULD be
configurable.
In some networks, the operator may still want links with maximum
metric (0xffff) to be treated as reachable. For example, when the
cost of links is automatically computed based on the inverse of the
link's bandwidth and and there is a mix of low-speed and high-speed
links, the computation may result in the maximum metric. In this
case, OSPF routers supporting this specification can disable the
Unreachable Link support capability and still treat links with
maximum metric as reachable.
It is also RECOMMENDED that implementations supporting this document
and auto-costing limit the maximum computed cost to
MaxReachableLinkMetric (0xfffe).
4.2. YANG Data Model
YANG [RFC7950] is a data definition language used to define the
contents of a conceptual data store that allows networked devices to
be managed using NETCONF [RFC6241] or RESTCONF [RFC8040].
This section defines three YANG modules. Module iana-ospf-
functional-cap-bits defines the identities for OSPF Functional
Capabilities as per the "OSPF Router Functional Capability Bits" IANA
registry [IANA-OSPF-FC-Bits]. Module ietf-ospf-functional-capability
and module ietf-ospf-unreachable-links can be used to configure and
manage the usage of OSPF LSLinkInfinity for unreachable links as
defined in this document, which augments the OSPF YANG data model
[RFC9129] and the YANG Data Model for Routing Management [RFC8349].
This document uses the graphical representation of data model per
[RFC8340].
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4.2.1. Tree for OSPF Functional Capability
The following shows the tree diagram of the module for OSPF
Functional Capability:
module: ietf-ospf-functional-capability
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
/ospf:database/ospf:area-scope-lsa-type
/ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
/ospf:ospfv2/ospf:ospfv2/ospf:body/ospf:opaque
/ospf:ri-opaque/ospf:router-capabilities-tlv:
+--ro router-functional-capabilities
+--ro functional-capability* identityref
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/ospf:ospf/ospf:database
/ospf:as-scope-lsa-type/ospf:as-scope-lsas
/ospf:as-scope-lsa/ospf:version/ospf:ospfv2/ospf:ospfv2
/ospf:body/ospf:opaque/ospf:ri-opaque
/ospf:router-capabilities-tlv:
+--ro router-functional-capabilities
+--ro functional-capability* identityref
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/ospf:ospf/ospf:database
/ospf:as-scope-lsa-type/ospf:as-scope-lsas
/ospf:as-scope-lsa/ospf:version/ospf:ospfv3/ospf:ospfv3
/ospf:body/ospf:router-information
/ospf:router-capabilities-tlv:
+--ro router-functional-capabilities
+--ro functional-capability* identityref
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
/ospf:database/ospf:area-scope-lsa-type
/ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
/ospf:ospfv3/ospf:ospfv3/ospf:body/ospf:router-information
/ospf:router-capabilities-tlv:
+--ro router-functional-capabilities
+--ro functional-capability* identityref
4.2.2. Tree for OSPF Advertising Unreachable Links
The following shows the tree diagram of the module for OSPF
Advertising Unreachable Links:
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module: ietf-ospf-unreachable-links
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/ospf:ospf:
+--rw unreachable-link-advertisement
+--rw enabled? boolean
4.2.3. IANA Module for OSPF Functional Capability Bits
IANA has created a registry titled "OSPF Router Functional Capability
Bits" under the "Open Shortest Path First (OSPF) Parameters" registry
group to identify OSPF Router Functional Capabilities. Module iana-
ospf-functional-cap-bits is an IANA-maintained module, which defines
the identities for the OSPF Functional Capabilities as in the IANA
"OSPF Router Functional Capability Bits" registry.
This module is maintained by IANA and will be updated if and when
there is any change to the registry.
This document defines the initial version of the IANA-maintained YANG
module for OSPF Router Functional Capabilities that mirrors the IANA
"OSPF Router Functional Capability Bits" registry
[IANA-OSPF-FC-Bits].
<CODE BEGINS> file "iana-ospf-functional-cap-bits@2025-09-28.yang"
module iana-ospf-functional-cap-bits {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:"
+ "iana-ospf-functional-cap-bits";
prefix iana-ospf-fc-bits;
organization
"Internet Assigned Numbers Authority (IANA)";
contact
"Internet Assigned Numbers Authority
ICANN
12025 Waterfront Drive, Suite 300
Los Angeles, CA 90094-2536
United States of America
Tel: +1 310 301 5800
<mailto:iana@iana.org>";
description
"This YANG module defines the identities for OSPF Router
Functional Capabilities.
This YANG module is maintained by IANA and reflects the 'OSPF
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Router Functional Capability Bits' registry.
Copyright (c) 2025 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Revised BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
All revisions of IETF and IANA published modules can be found
at the YANG Parameters registry group
(https://www.iana.org/assignments/yang-parameters).
This initial version of this YANG module is part of RFC XXXX
(https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
for full legal notices.
The latest version of this YANG module is available at
https://www.iana.org/assignments/yang-parameters.";
revision 2025-09-28 {
description
"Initial version";
reference
"RFC XXXX: Advertising Unreachable Links in OSPF";
}
identity functional-capability {
description
"Base identity for OSPF Router Functional Capabilities. The
functional capabilities are defined in IANA OSPF Router
Functional Capability Bits registry.";
}
identity unreachable-link {
base functional-capability;
description
"Indicates that the OSPF router is capable of advertising
unreachable links.";
reference
"RFC XXXX: Advertising Unreachable Links in OSPF";
}
}
<CODE ENDS>
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4.2.4. YANG Module for OSPF Functional Capability
The following is the YANG module for OSPF Functional Capability:
<CODE BEGINS> file "ietf-ospf-functional-capability@2025-09-28.yang"
module ietf-ospf-functional-capability {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:"
+ "ietf-ospf-functional-capability";
prefix ospf-fc;
import ietf-routing {
prefix rt;
reference
"RFC 8349: A YANG Data Model for Routing Management
(NMDA Version)";
}
import ietf-ospf {
prefix ospf;
reference
"RFC 9129: YANG Data Model for the OSPF Protocol";
}
import iana-ospf-functional-cap-bits {
prefix iana-ospf-fc-bits;
reference
"RFC XXXX: Advertising Unreachable Links in OSPF";
}
organization
"IETF Link State Routing (LSR) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/lsr/>
WG List: <mailto:lsr@ietf.org>
Author: Yingzhen Qu
<mailto:yqu@futurewei.com>
Author: Acee Lindem
<mailto:acee.ietf@gmail.com>
Author: Liyan Gong
<mailto:gongliyan@chinamobile.com>
Author: Weiqiang Cheng
<mailto:chengweiqiang@chinamobile.com>
Author: Changwang Lin
<mailto:linchangwang.04414@h3c.com>
Author: Ran Chen
<mailto:chen.ran@zte.com.cn>";
description
"This YANG module defines the operational state for
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Functional Capability in OSPF as defined in RFC 7770.
Copyright (c) 2025 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Revised BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
All revisions of IETF and IANA published modules can be found
at the YANG Parameters registry group
(https://www.iana.org/assignments/yang-parameters).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
revision 2025-09-28 {
description
"Initial version";
reference
"RFC XXXX: Advertising Unreachable Links in OSPF";
}
grouping router-functional-capabilities {
description
"Grouping for OSPF router capabilities TLV types.";
reference
"RFC 7770: Extensions to OSPF for Advertising Optional
Router Capabilities";
container router-functional-capabilities {
leaf-list functional-capability {
type identityref {
base iana-ospf-fc-bits:functional-capability;
}
description
"List of functional capabilities. This list
contains the identities for the functional
capabilities supported by the router.";
}
description
"OSPF Router Functional identity definitions.";
}
}
augment "/rt:routing/"
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+ "rt:control-plane-protocols/rt:control-plane-protocol/"
+ "ospf:ospf/ospf:areas/"
+ "ospf:area/ospf:database/"
+ "ospf:area-scope-lsa-type/ospf:area-scope-lsas/"
+ "ospf:area-scope-lsa/ospf:version/ospf:ospfv2/"
+ "ospf:ospfv2/ospf:body/ospf:opaque/"
+ "ospf:ri-opaque/ospf:router-capabilities-tlv" {
when "derived-from-or-self(/rt:routing/"
+ "rt:control-plane-protocols/"
+ "rt:control-plane-protocol/rt:type, 'ospf:ospfv2')" {
description
"This augmentation is only valid for OSPFv2.";
}
description
"OSPFv2 Opaque Area-Scoped Router-Information LSA Router
Functional capabilities.";
uses router-functional-capabilities;
reference
"RFC 7770: Extensions to OSPF for Advertising Optional
Router Capabilities";
}
augment "/rt:routing/"
+ "rt:control-plane-protocols/rt:control-plane-protocol/"
+ "ospf:ospf/ospf:database/"
+ "ospf:as-scope-lsa-type/ospf:as-scope-lsas/"
+ "ospf:as-scope-lsa/ospf:version/ospf:ospfv2/"
+ "ospf:ospfv2/ospf:body/ospf:opaque/"
+ "ospf:ri-opaque/ospf:router-capabilities-tlv" {
when "derived-from-or-self(/rt:routing/"
+ "rt:control-plane-protocols/"
+ "rt:control-plane-protocol/rt:type, 'ospf:ospfv2')" {
description
"This augmentation is only valid for OSPFv2.";
}
description
"OSPFv2 Opaque AS-Scoped Router-Information LSA Router
Functional capabilities.";
uses router-functional-capabilities;
reference
"RFC 7770: Extensions to OSPF for Advertising Optional
Router Capabilities";
}
augment "/rt:routing/"
+ "rt:control-plane-protocols/rt:control-plane-protocol/"
+ "ospf:ospf/ospf:database/"
+ "ospf:as-scope-lsa-type/ospf:as-scope-lsas/"
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+ "ospf:as-scope-lsa/ospf:version/ospf:ospfv3/"
+ "ospf:ospfv3/ospf:body/ospf:router-information/"
+ "ospf:router-capabilities-tlv" {
when "derived-from-or-self(/rt:routing/"
+ "rt:control-plane-protocols/"
+ "rt:control-plane-protocol/rt:type, 'ospf:ospfv3')" {
description
"This augmentation is only valid for OSPFv3.";
}
description
"OSPFv3 Area-Scoped Router-Information LSA Router
Functional capabilities.";
uses router-functional-capabilities;
reference
"RFC 7770: Extensions to OSPF for Advertising Optional
Router Capabilities";
}
augment "/rt:routing/"
+ "rt:control-plane-protocols/rt:control-plane-protocol/"
+ "ospf:ospf/ospf:areas/"
+ "ospf:area/ospf:database/"
+ "ospf:area-scope-lsa-type/ospf:area-scope-lsas/"
+ "ospf:area-scope-lsa/ospf:version/ospf:ospfv3/"
+ "ospf:ospfv3/ospf:body/ospf:router-information/"
+ "ospf:router-capabilities-tlv" {
when "derived-from-or-self(/rt:routing/"
+ "rt:control-plane-protocols/"
+ "rt:control-plane-protocol/rt:type, 'ospf:ospfv3')" {
description
"This augmentation is only valid for OSPFv3.";
}
description
"OSPFv3 AS-Scoped Router-Information LSA Router
Functional capabilities.";
uses router-functional-capabilities;
reference
"RFC 7770: Extensions to OSPF for Advertising Optional
Router Capabilities";
}
}
<CODE ENDS>
4.2.5. YANG Module for OSPF Advertising Unreachable Links
The following is the YANG module for OSPF Advertising Unreachable
Links:
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<CODE BEGINS> file "ietf-ospf-unreachable-links@2025-09-28.yang"
module ietf-ospf-unreachable-links {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:"
+ "ietf-ospf-unreachable-links";
prefix ospf-unreach-link;
import ietf-routing {
prefix rt;
reference
"RFC 8349: A YANG Data Model for Routing Management
(NMDA Version)";
}
import ietf-ospf {
prefix ospf;
reference
"RFC 9129: YANG Data Model for the OSPF Protocol";
}
organization
"IETF Link State Routing (LSR) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/lsr/>
WG List: <mailto:lsr@ietf.org>
Author: Yingzhen Qu
<mailto:yqu@futurewei.com>
Author: Acee Lindem
<mailto:acee.ietf@gmail.com>
Author: Liyan Gong
<mailto:gongliyan@chinamobile.com>
Author: Weiqiang Cheng
<mailto:chengweiqiang@chinamobile.com>
Author: Changwang Lin
<mailto:linchangwang.04414@h3c.com>
Author: Ran Chen
<mailto:chen.ran@zte.com.cn>";
description
"This YANG module defines the configuration and operational
state for Advertising Unreachable Links in OSPF as defined
in RFC XXXX.
Copyright (c) 2025 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Revised BSD License
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set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
All revisions of IETF and IANA published modules can be found
at the YANG Parameters registry group
(https://www.iana.org/assignments/yang-parameters).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
revision 2025-09-28 {
description
"Initial version";
reference
"RFC XXXX: Advertising Unreachable Links in OSPF";
}
augment "/rt:routing/rt:control-plane-protocols"
+ "/rt:control-plane-protocol/ospf:ospf" {
when "derived-from-or-self(../rt:type, 'ospf:ospfv2') or "
+ "derived-from-or-self(../rt:type, 'ospf:ospfv3')" {
description
"This augments the OSPF routing protocol when used.";
}
description
"This augments OSPF protocol with unreachable link
advertisement.";
container unreachable-link-advertisement {
leaf enabled {
type boolean;
default "false";
description
"Controls advertisement of unreachable links.
It is enabled when set to true and desabled
when set to false.";
}
description
"OSPF unreachable link advertisement parameters.";
}
}
}
<CODE ENDS>
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5. Security Considerations
The document does not introduce any new security issues for the OSPF
protocol. The security considerations for [RFC2328],[RFC5340],
[RFC6987], and [RFC7770] are applicable to protocol extension.
The ietf-ospf-unreachable-links YANG module and the ietf-ospf-
functional-capability YANG module each define a data model that is
designed to be accessed via YANG-based management protocols, such as
NETCONF [RFC6241] and RESTCONF [RFC8040]. These YANG-based
management protocols (1) have to use a secure transport layer (e.g.,
SSH [RFC4252], TLS [RFC8446], and QUIC [RFC9000]) and (2) have to use
mutual authentication.
The NETCONF Access Control Model (NACM) [RFC8341] provides the means
to restrict access for particular NETCONF or RESTCONF users to a pre-
configured subset of all available NETCONF or RESTCONF protocol
operations and content.
The following data nodes defined in the ietf-ospf-unreachable-links
YANG module that are writable/creatable/deletable (i.e., config true,
which is the default). The modifications to these data nodes without
proper protection can have prevent interpreting the OSPF
LSLinkInfinity metric as unreachable.
/ospf:ospf/ospf-unreach-link:unreachable-link-advertisement/ospf-
unreach-link:enabled
Some of the readable data nodes in the ietf-ospf-unreachable-links
YANG module may be considered sensitive or vulnerable in some network
environments. Exposure of the OSPF link state database may be useful
in mounting a Denial-of-Service (DoS) attacks. These are the
readable data nodes:
/ospf:ospf/ospf-unreach-link:unreachable-link-advertisement/ospf-
unreach-link:enabled
6. IANA Considerations
6.1. Registering OSPF Router Functional Capability Bits
This document defines a new bit in the registry "OSPF Router
Functional Capability Bits":
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+============+==========================+===============+
| Bit Number | Capability Name | Reference |
+============+==========================+===============+
| 0(TBD) | Unreachable Link support | This document |
+------------+--------------------------+---------------+
Table 2
6.2. Registering YANG Modules
The IANA is requested to assign three new URIs from the IETF XML
registry ([RFC3688]). Authors are suggesting the following URIs:
URI: urn:ietf:params:xml:ns:yang:iana-ospf-functional-cap-bits
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace
URI: urn:ietf:params:xml:ns:yang:ietf-ospf-functional-capability
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace
URI: urn:ietf:params:xml:ns:yang:ietf-ospf-unreachable-links
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace
This document also requests three new YANG module names in the YANG
Module Names registry ([RFC6020]) with the following suggestion :
Name: iana-ospf-functional-cap-bits
Maintained by IANA? Y
Namespace: urn:ietf:params:xml:ns:yang:iana-ospf-functional-cap-bits
Prefix: iana-ospf-fc-bits
Reference: RFC XXXX
Name: ietf-ospf-functional-capability
Maintained by IANA? N
Namespace: urn:ietf:params:xml:ns:yang:
ietf-ospf-functional-capability
Prefix: ospf-fc
Reference: RFC XXXX
Name: ietf-ospf-unreachable-links
Maintained by IANA? N
Namespace: urn:ietf:params:xml:ns:yang:ietf-ospf-unreachable-links
Prefix: ospf-unreach-link
Reference: RFC XXXX
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6.3. IANA Module for OSPF Functional Capability Bits
This document defines the initial version of the IANA-maintained
"iana-ospf-functional-cap-bits" YANG module (Section 4.2). The most
recent version of the YANG module is available from the "YANG
Parameters" registry [IANA-YANG-Parameters].
IANA is requested to add this note to the registry:
| New values must not be directly added to the "iana-ospf-
| functional-cap-bits" YANG module. They must instead be added to
| the "OSPF Router Functional Capability Bits" registry in the "Open
| Shortest Path First (OSPF) Parameters" registry group
| [IANA-OSPF-FC-Bits].
When a value is added to the "OSPF Router Functional Capability Bits"
registry, a new "identity" statement needs to be added to the "iana-
ospf-functional-cap-bits" YANG module. The name of the "identity"
MUST be the name as provided in the registry. The "identity"
statement should have the following sub-statements defined:
"base": Contains 'functional-capability'.
"description": Replicates the description from the registry.
"reference": Replicates the reference(s) from the registry with
the title of the document(s) added.
When the "iana-ospf-functional-cap-bits" YANG module is updated, a
new "revision" statement with a unique revision date must be added in
front of the existing revision statements. The "revision" statement
MUST contain both "description" and "reference" substatements as
follows.
The "description" substatement captures what changed in the revised
version. Typically, the description enumerates the changes such as
udpates to existing entries (e.g., update a description or a
reference) or notes which identities were added or had their status
changed (e.g., deprecated, discouraged, or obsoleted).
The "reference" substatement points specifically to the published
module (i.e., IANA_FOO_URL_With_REV). It may also point to an
authoritative event triggering the update to the YANG module. In all
cases, this event is cited from the underlying IANA registry. If the
update is triggered by an RFC, that RFC must also be included in the
"reference" substatement.
IANA is requested to add this note to [IANA-OSPF-FC-Bits]:
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| When this registry is modified, the YANG module "iana-ospf-
| functional-cap-bits" must be updated as defined in RFC XXXX.
7. Contributors
The following individuals have contributed to this document:
Mengxiao Chen
New H3C Technologies
China
Email: chen.mengxiao@h3c.com
Yanrong Liang
Ruijie Networks Co., Ltd.
China
Email: liangyanrong@ruijie.com.cn
8. Acknowledgments
Thanks to Yingzhen Qu for providing the YANG model.
Thanks to Dhruv Dhody for OPS Directorate review and comments.
9. References
9.1. Normative References
[IANA-OSPF-FC-Bits]
IANA, "OSPF Router Functional Capability Bits",
<https://www.iana.org/assignments/ospf-parameters>.
[IANA-YANG-Parameters]
IANA, "YANG Module Names",
<https://www.iana.org/assignments/yang-parameters>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
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[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007,
<https://www.rfc-editor.org/info/rfc4915>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <https://www.rfc-editor.org/info/rfc7770>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
<https://www.rfc-editor.org/info/rfc8341>.
[RFC8349] Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
Routing Management (NMDA Version)", RFC 8349,
DOI 10.17487/RFC8349, March 2018,
<https://www.rfc-editor.org/info/rfc8349>.
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[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.
[RFC9129] Yeung, D., Qu, Y., Zhang, Z., Chen, I., and A. Lindem,
"YANG Data Model for the OSPF Protocol", RFC 9129,
DOI 10.17487/RFC9129, October 2022,
<https://www.rfc-editor.org/info/rfc9129>.
9.2. Informative References
[RFC4252] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
January 2006, <https://www.rfc-editor.org/info/rfc4252>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987,
DOI 10.17487/RFC6987, September 2013,
<https://www.rfc-editor.org/info/rfc6987>.
[RFC7308] Osborne, E., "Extended Administrative Groups in MPLS
Traffic Engineering (MPLS-TE)", RFC 7308,
DOI 10.17487/RFC7308, July 2014,
<https://www.rfc-editor.org/info/rfc7308>.
[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/info/rfc8340>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8770] Patel, K., Pillay-Esnault, P., Bhardwaj, M., and S.
Bayraktar, "Host Router Support for OSPFv2", RFC 8770,
DOI 10.17487/RFC8770, April 2020,
<https://www.rfc-editor.org/info/rfc8770>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
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[RFC9350] Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
DOI 10.17487/RFC9350, February 2023,
<https://www.rfc-editor.org/info/rfc9350>.
Authors' Addresses
Liyan Gong
China Mobile
China
Email: gongliyan@chinamobile.com
Weiqiang Cheng
China Mobile
China
Email: chengweiqiang@chinamobile.com
Changwang Lin
New H3C Technologies
China
Email: linchangwang.04414@h3c.com
Acee Lindem
Arrcus, Inc.
United States of America
Email: acee.ietf@gmail.com
Ran Chen
ZTE Corporation
China
Email: chen.ran@zte.com.cn
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